Olfactory Detection Thresholds in Children with Autism Spectrum Disorders Using Pulse Ejection Systems

Background:  Sensory abnormalities occur in patients with autism spectrum disorder (ASD) worldwide. Unusual reactions to odor stimuli are well known sensory symptoms in ASD. However, olfactory laboratory tests have provided limited information about such abnormalities in ASD. Conventional techniques for measurement of olfactory function have problems of dispersion of scents in the air, and tedious examination.

Objectives:  In this study, we used an olfactory measurement that uses pulse ejection. Pulse ejection systems are capable of presenting scents for a short duration even at the picoliter level. Unlike existing techniques for measurement of olfactory function, our olfactory display employs pulse ejection and measures olfaction by varying the quantity of ejected odorant. The odor detection threshold can be quantified by the ejection quantity. This allows the pulse ejection system to quantify the human ability to smell with great precision. This study examined odor detection thresholds with this new system for measurement of olfactory function in a sample of adolescents with ASD.

Methods:  Of the 30 participants, 15 were patients with ASD (3 women, 12 men) and 15, controls (3 females, 12 males). They were referred to our laboratory in August 2014 for examination of sensory symptoms. All the patients satisfied the diagnostic criteria for ASD in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (American Psychiatric Association, 2013). To exclude other psychiatric diagnoses, the Mini-International Neuropsychiatric Interview for Children and Adolescents was conducted by a licensed pediatric-psychiatric clinician. To obtain data from normal age-matched healthy controls (HC), healthy schoolchildren and adolescents aged 8–18 years were recruited from the community. None had a below-average IQ, physical problems, or psychiatric psychopathology. Odor detection thresholds were assessed using the olfactory measurement system with olfactory display by pulse ejection. The equipment comprised an ejection head that could hold three small and one large tank, for a maximum of four scents. We used isoamyl acetate and ethyl butyrate flavor for the odorants. The subjects’ scores ranged between 10 and 160. Statistical analysis was performed with the Statistical Package for the Social Sciences, version 15.0. Descriptive statistics were used for the samples. Age differences between the groups were analyzed using the independent samples t-test. Differences in odor detection thresholds were analyzed using the Mann–Whitney U-Test.

Results:  There were no significant differences between groups with regard to mean age and gender proportion. The odor detection threshold for both flavors was significantly impaired in the ASD group compared to the HCs (for the isoamyl acetate flavor; ASD, 75.6 ± 57.3 vs. HC, 17.8 ± 13.6; p < 0.01 and for the ethyl butyrate flavor; ASD, 78.9 ± 52.1 vs. HC, 12.2 ± 4.6; p< 0.01).

Conclusions:  Odor detection for the isoamyl acetate and ethyl butyrate flavors was impaired in adolescents with ASD. Implications for further research are discussed.